'88 IROC 5.7 (L98) is running 1300 rpms too high. Do you think voltage is too low? Bad ground? Any ideas?

 

The tachs on these cars are well known for being wayyyyy off after a while. There is a resistor chip thing on the back of them that gets shot out at some point. There was a thread on this a few weeks ago, look it up, theres helpful info in there.

 

Also clean the carbon from the inside of the throttle blades.